Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000 FXUS66 KSEW 191031 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 331 AM PDT Tue Sep 19 2017 .SYNOPSIS...Low pressure aloft will remain over the region through Wednesday for cool and unsettled conditions. High pressure aloft will gradually move over the area from the west the latter part of the week for a drying and warming trend. && .SHORT TERM... There were quite a few showers over the CWA at this time. A few of these showers were heavy and likely contained small hail. There has also been lightning strikes off the coast of Grays Harbor County. Therefore, went on ahead and put thunderstorms in the forecast for the far southwest part of the forecast area today. The air mass should stabilize by early this evening. The temperature has been hovering at 32 degrees at Paradise for the past several hours. It is likely that the precipitation has been falling as snow during these hours. Unfortunately, the snow sensor appeared to be out of service. It looks like about four inches, possibly five inches, of snow has fallen at Paradise thus far, per the liquid accumulation. The temp should stay near freezing through much of this morning, so went on ahead and issued a Winter Storm Warning for the Cascades above 5000 feet in Pierce and Lewis Counties. Meanwhile, a broad area of low pressure aloft will keep the air mass over the region cool and unsettled through Wednesday. Overall, it appeared that the heaviest precipitation will occur over the southern half of the CWA during this time frame. Temps will remain below normal. Heights/thicknesses will gradually rise Wednesday night through Thursday as the upper level trof slowly slides off to the east. This will allow northerly flow aloft to become established over the region. However, the flow will remain weakly cyclonic. This combined with lingering moisture will result in a chance of showers through Thursday. .LONG TERM... There might be a few light showers over the interior on Friday under continued weak cyclonic flow aloft; otherwise, expect an upper level ridge to build over the area from the west on Friday for a drying trend. An upper ridge over the northeast Pacific will give dry northerly flow to Western Washington Saturday through Monday. Highs will warm back to near normal. Schneider/05 && .AVIATION...Upper level trough over the area with northwesterly flow aloft. Air mass moist and unstable with onshore flow. Multiple cloud layers over Western Washington between 2000 and 6000 feet with ceilings near 2000 feet becoming predominate after 12z. Ceilings improving into the 3500 to 4500 foot range this afternoon into the evening hours. Thunderstorm possible near the Coast throughout the day. KSEA...Ceilings near 2000 feet improving to near 4000 feet this afternoon. Could see visibilities briefly lower to 3-5sm in showers. Southerly winds 5 to 10 knots through Tuesday afternoon. Felton && .MARINE...Low pressure will remain over the region through Thursday. A trough will move the area late tonight and Wednesday morning. Strongest winds with this trough will be south of the area. Winds will becoming light northerly on Wednesday as low pressure passes to the south. High pressure will build into the area Friday into Saturday. Swell over the coastal waters in the 12 to 14 foot range will subside below 10 feet tonight and remain below 10 feet into the weekend. Felton && .SEW WATCHES/WARNINGS/ADVISORIES... WA...Winter Storm Warning until 5 PM PDT this afternoon for Cascades of Pierce and Lewis Counties above 5000 feet. PZ...Small Craft Advisory until 11 AM PDT this morning for Coastal Waters From Cape Flattery To James Island 10 To 60 Nm- Coastal Waters From James Island To Point Grenville 10 To 60 Nm-Coastal Waters From Point Grenville To Cape Shoalwater 10 To 60 Nm. Small Craft Advisory for hazardous seas from 11 AM this morning to 5 PM PDT this afternoon for Coastal Waters From Cape Flattery To James Island 10 To 60 Nm-Coastal Waters From James Island To Point Grenville 10 To 60 Nm-Coastal Waters From Point Grenville To Cape Shoalwater 10 To 60 Nm. Small Craft Advisory for rough bar until 8 PM PDT this evening for Grays Harbor Bar. Small Craft Advisory for hazardous seas until 5 PM PDT this afternoon for Coastal Waters From Cape Flattery To James Island Out 10 Nm-Coastal Waters From James Island To Point Grenville Out 10 Nm-Coastal Waters From Point Grenville To Cape Shoalwater Out 10 Nm-West Entrance U.S. Waters Strait Of Juan De Fuca. && $$ www.weather.gov/seattle An illustrated version of this forecast discussion can be seen at www.wrh.noaa.gov/sew/gafd/latest_webafd.html

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